The present invention relates to forklift vehicles having an integral steering and drive mechanism.
In the past, steering material handling forklift trucks was accomplished by utilizing a single steer/drive unit. That is, the vehicle had a single wheel used for both driving and steering. The steering angle of the wheel was controlled through an offset steer motor coupled to the drive unit through a gear reducer, a pinion gear directly coupled or coupled through a connecting chain. The steer motor was usually an electric motor or a hydraulic motor.
Where an electric motor drive was used, a control circuit was employed to determine the direction of motor rotation and for varying the applied voltage(s).
Where a hydraulic motor was implemented, an electric motor was used to drive a hydraulic pump that supplied fluid to the hydraulic motor. In the case of manually controlled hydraulic systems, manually operated rotary valves were used for determining the direction of hydraulic motor rotation and for varying the rate of hydraulic fluid flow. In the case of electro-hydraulic systems, an electric signaling device was used in conjunction with a servo or proportioning valve for determining the direction of hydraulic motor rotation and for varying the rate of hydraulic fluid flow.
Generally, both of the aforementioned systems also required a steer motor speed sensor connected to the shaft of the steer motor, and a steering angle sensor connected to the drive unit, in order to complete the circuit loop in the control system.
The primary purpose of the speed motor sensor was to prevent harmonic oscillation due to the mechanical coupling backlash in the gear reducer, pinion gear directly coupled or coupled through the drive chain between the steering motor and the drive unit.
The present invention seeks to integrate the traction motor and steering motor into a single steer/drive system in order to eliminate the need for a gear reducer and pinion gear directly coupled or coupled through a drive chain between the two motors. This in turn eliminates the need for a separate speed motor sensor.
The present invention not only eliminates many parts in the traditional steer drive arrangement, but it also has the advantage of eliminating the troublesome harmonic oscillations inherent within the conventional steer system. Direct motor coupling makes such oscillations impossible.